In order to capture a reasonably clear image of a target, the one or more lenses need to be properly positioned in order for the image to be received at the image detector with sufficient clarity, regardless as to whether the image is being captured on film or digitally, such as using a CCD. Depending on the distance that the intended target is away from the image capturing system, such as a camera, the image capturing system will detect a focused image, when the lens is appropriately positioned within the system, and allow for the capture of a sharp image. Focusing a image capturing system on the target can involve the movement of one or more lenses.
Several methods are known in the art for focusing an image capturing system relative to the target. In one such method, a user focuses the lens manually on a target. Manually focusing the lens introduces a significant amount of set up time, when the position of the lens is manually adjusted in order to focus on the intended target. Depending on the nature of the image being captured, for the casual photographer the moment may be lost before the user has had a chance to bring the image into focus. Several other methods describe automatically focusing the image capturing system relative to the target. These methods include sequentially capturing the target in multiple frames, while varying the lens position and determining whether the adjustment makes the focus better or worse. In image capturing systems involving such methods, a processor captures the image in a first frame at a first lens position and a second frame at a second lens position. The images of the first frame and the second frame are compared and a further adjusted position for the lens is determined thereafter. Generally if the image clarity is improving, then an adjustment of the lens position continues in the same general direction. However, if the image clarity is made worse, then an adjustment of the lens will generally be made in the opposite direction. This process of comparing images of a pair of frames is repeated till an image having the desired level of sharpness and contrast is captured, or such as when there is no further improvement, when the lens position is adjusted in either direction. Such methods may take a significant amount of time in focusing on the target, depending upon the rate at which each adjustment can be made. Where a single adjustment is made in association with each captured image, the amount of time in focusing on the target is closely linked to the image capture rate, or in other words the number of frames captured per second. For at least some high resolution cameras, or as a camera attempt to capture images at increased resolution, frames rates may be relatively lower.
Further, these methods generally follow the same method of focusing regardless as to whether the captured image is primarily composed of color, or is largely black and white. Additionally, the methods will similarly generally follow the same method of focusing regardless as to whether an initial determination of focus identifies relatively constant localized contrast values across the entire image, or whether there are meaningful differences. In some instances, an assumption concerning the type of image can be made for purposes of focusing an image capturing system relative to a target, depending upon whether a black and white or a color target is detected, which can allow for an arrival at the proper focus in less time as contrasted with an automatic focusing method which may attempt to apply an auto focus method and system, which is ambivalent as to the color content of an image, which may have been detected. Hence, a time might be wasted if the same method of focusing is used for focusing regardless of the nature of the color content contained within the image.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.